When an oil well is drilled, the drill bit is positioned at the bottom of the drill string and a set of heavy, thick walled drill collars is located in the drill string immediately above the drill bit. The drill collars add stiffness to the drill string, control the weight on the drill bit, and thereby control lateral drift or deviation of the drill string. The number of drill collars in a drill string will vary depending on the depth of the well, the particular formations encountered and so on.
During the drilling of an oil well which is fairly deep, there is ample opportunity for the drill string to be seized at the drill collars. Typically, this will happen when the sidewall of the hole collapses and dirt falls into the annulus around the pipe, thereby seizing the drill string at the drill collars. Even if the hole partially collapses 2 or 3 thousand feet above, the dirt, rocks, etc. which fall into the hole will accumulate just above the drill bit and thereby seize the drill string near the drill collars. Alternately, the drill bit will be deflected somewhat and drift from its intended course, thereby placing the drill string in a bind. So to speak, it forms a key seat where the drill collars are forced to the side of a part of the hole which was previously drilled, and they then tend to lock against the side of the hole. This is binding on the drill string.
When, for any of the above mentioned reasons or other reasons not named, the drill string is seized, it is necessary to free it up. There are several ways of doing this. One way is to use a jar in the drill string for purposes of imparting a substantial impact to the drill string in the immediate vicinity of the place where it is stuck. Since sticking typically occurs just above the drill bit at the drill collars, a jar mechanism in the drill string is quite advantageous.
The present invention is a jar which is installed in a drill string. It is located among the drill collars. It functions as a drill collar itself during routine drilling operations. When the drill string is stuck, the present invention can be used in conjunction with the rotary drilling apparatus to impart a jarring impact to the drill string for jarring it loose from the stuck condition.
Other devices have been provided heretofore for jars to be used in drill strings. It is believed that the present invention constitutes a significant advance over them. It is relatively simple in retrospect and, therefore, less costly in manufacturing. In addition, the present invention utilizes two basic tubular members which further simplies and defines it over the known devices. Known patents of interest are U.S. Pat. Nos. 3,001,596; 1,627,321; 1,672,464; 2,819,878; 2,819,879; 3,200,895; and 3,371,730.